Homeobox genes generally encode transcription factors involved in regulating developmental processes. In the pineal gland, a brain structure devoted to nocturnal melatonin synthesis, a number of homeobox genes are also expressed postnatally; among these is the LIM homeobox 4 gene (Lhx4). We here report that Lhx4 is specifically expressed in the postnatal pineal gland of rats and humans. Circadian analyses revealed a fourfold rhythm in Lhx4 expression in the rat pineal gland, with rhythmic expression detectable from postnatal day 10. Pineal Lhx4 expression was confirmed to be positively driven by adrenergic signaling, as evidenced by in vivo modulation of Lhx4 expression by pharmacological (isoprenaline injection) and surgical (superior cervical ganglionectomy) interventions. In cultured pinealocytes, Lhx4 expression was upregulated by cyclic AMP, a second messenger of norepinephrine. By use of RNAscope technology, Lhx4 transcripts were found to be exclusively localized in melatonin-synthesizing pinealocytes. This prompted us to investigate the possible role of Lhx4 in regulation of melatonin-producing enzymes. By use of siRNA technology, we knocked down Lhx4 by 95% in cultured pinealocytes; this caused a reduction in transcripts encoding the melatonin-producing enzyme arylalkylamine N-acetyl transferase (Aanat). Screening the transcriptome of siRNA-treated pinealocytes by RNAseq revealed a significant impact of Lhx4 on the phototransduction pathway and on transcripts involved in development of the nervous system and photoreceptors. These data suggest that rhythmic expression of Lhx4 in the pineal gland is controlled via an adrenergic-cyclic AMP mechanism and that Lhx4 acts to promote nocturnal melatonin synthesis.

中文翻译：

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大鼠松果体中的 Lhx4 同源盒转录物：肾上腺素能调节和对编码褪黑激素合成酶的转录物的影响。

同源盒基因通常编码参与调节发育过程的转录因子。在松果体，一种致力于夜间褪黑激素合成的大脑结构，许多同源盒基因也在出生后表达。其中包括 LIM 同源框 4 基因 (Lhx4)。我们在此报告 Lhx4 在大鼠和人类的出生后松果体中特异性表达。昼夜节律分析揭示了大鼠松果体中 Lhx4 表达的四倍节律，从出生后第 10 天可检测到节律性表达。松果体 Lhx4 表达被证实由肾上腺素能信号传导正向驱动，药理学（异丙肾上腺素）对 Lhx4 表达的体内调节证明了这一点注射）和手术（颈上神经节切除术）干预。在培养的松果体细胞中，Lhx4 表达被环 AMP 上调，去甲肾上腺素的第二信使。通过使用 RNAscope 技术，发现 Lhx4 转录本仅位于合成褪黑激素的松果体细胞中。这促使我们研究 Lhx4 在调节褪黑激素产生酶中的可能作用。通过使用 siRNA 技术，我们在培养的松果体细胞中敲低了 95% 的 Lhx4；这导致编码褪黑激素产生酶芳基烷基胺 N-乙酰转移酶 (Aanat) 的转录物减少。通过 RNAseq 筛选 siRNA 处理的松果体细胞的转录组揭示了 Lhx4 对光转导途径以及参与神经系统和光感受器发育的转录物的显着影响。